The present invention relates to voltage regulator controller circuits. More particularly, the present invention relates to circuits and methods for providing both a soft-start function and a short-circuit timer function using a single package pin in a voltage regulator controller circuit.
The purpose of a voltage regulator is to provide a predetermined and substantially constant output voltage to a load from a voltage source which may be poorly-specified or fluctuating. In a typical linear voltage regulator, the voltage at the regulator output is regulated by controlling the flow of current passing through a pass element (such as a power transistor) from the voltage source to the load. In typical switching voltage regulators, the voltage at each regulator output is regulated by controlling the width of current pulses passing through an inductive energy storage element (such as an inductor) from the voltage source to the load. In both of these types of voltage regulators, a voltage regulator controller circuit must be employed to control the flow of current in the linear regulators and the width of the current pulses in the switching regulators.
One feature typically found in switching-based voltage regulator controller circuits is a soft-start function. A soft-start function typically reduces current surges at a voltage source by gradually increasing the current limit of the voltage regulator controller circuit so that the current drawn from the voltage source gradually builds from a low level to a normal operating level. In some implementations of a soft-start function, a package pin is used to enable a voltage regulator designer to control whether the soft-start function is to be active and, if so, to control the rate at which the soft-start function increases the current limit of the voltage regulator controller circuit. One problem with using a package pin for such a soft-start function is that once the soft-start function has performed its task, the pin is no longer in active use in the circuit.
Another feature found in some voltage regulator controller circuits is a short-circuit latch off function. This function protects a voltage regulator from short circuits at the output of the voltage regulator by causing the regulator to be shutdown when a short circuit at the output of the voltage regulator is detected. One problem with the known short-circuit latch off function in voltage regulator controller circuits is it's susceptibility to noise and brief periods of large current surges. When either of these conditions occur, these known voltage regulator controller circuits may cause the voltage regulators to be shutdown even though the conditions were only temporary and not sufficient to damage the regulator. Another problem with known short-circuit latch off functions in voltage regulator controller circuits is that they are not externally controllable. In certain instances it is desirable to disable a short circuit latch off function, for example, when testing a circuit.
In view of the foregoing, it would be desirable to provide voltage regulator controller circuits that provide a soft-start function that utilizes an external pin to control the soft-start feature and that also allows the external pin to be used for other purposes once the soft-start period has passed.
It would also be desirable to provide voltage regulator controller circuits that provide a short circuit protection mechanism that is not subject to noise and brief periods of large current surges.
It would be further desirable to provide voltage regulator controller circuits that provide a short circuit protection mechanism that enables the mechanism to be disabled.
It would be even further desirable to provide voltage regulator controller circuits that provide a soft-start function and a short circuit protection mechanism that share a single package pin.